title: Performance of the pediatric index of mortality 2 (PIM-2) in cardiac and mixed intensive care units in a tertiary children's referral hospital in Italy.
abstract: BACKGROUND
  Mortality rate of patients admitted to Intensive Care Units is a widely adopted outcome indicator. Because of large case-mix variability, comparisons of mortality rates must be adjusted for the severity of patient illness at admission. The Pediatric Index of Mortality 2 (PIM-2) has been widely adopted as a tool for adjusting mortality rate by patients' case mix. The objective of this study was to assess the performance of PIM-2 in children admitted to intensive care units after cardiac surgery, other surgery, or for other reasons.
  
  
  METHODS
  This was a prospective cohort study, conducted in a 607 inpatient-bed tertiary-care pediatric hospital in Italy, with three pediatric intensive care Units (PICUs) and one cardiac Unit (CICU). In 2009-11, all consecutive admissions to PICUs/CICU of children aged 0-16 years were included in the study. Discrimination and calibration measures were computed to assess PIM-2 performance. Multivariable logistic regression analysis was used to assess the association of patients' main reason for intensive care admission (cardiac-surgical, other-surgical, medical), age, Unit and year with observed mortality, adjusting for PIM-2 score.
  
  
  RESULTS
  PIM-2 data collection was completed for 91.2% of total PICUs/CICU patient admissions (2912), and for 94.8% of patients who died in PICUs/CICU (129). Overall observed mortality was 4.4% (95% CI, 3.7-5.2), compared to 6.4% (95% CI, 5.5-7.3) expected mortality. Standardised mortality ratio was 0.7 (95% CI: 0.6-0.8). PIM-2 discrimination was fair (area under the curve, 0.79; 95% CI: 0.75-0.83). Calibration was less satisfactory, mainly because of the over two-fold overprediction of deaths in the highest risk group (114.7 vs 53; p < 0.001), and particularly in cardiac-surgical patients. Multivariable logistic analysis showed that risk of death was significantly reduced in cardiac-surgical patients and in those aged 1 month to 12 years, independently from PIM-2.
  
  
  CONCLUSIONS
  The children age distribution and the proportion of cardiac-surgical patients should be taken into account when interpreting SMRs estimated using the PIM-2 prediction model in different Units. A new calibration study of PIM-2 score might be needed, and more appropriate cardiac-focused risk-adjustment models should be developed. The role of age on risk of death needs to be further explored.
authors.forename: Marta Luisa
authors.initials: ML
authors.lastname: Ciofi degli Atti
authors.forename: Marina
authors.initials: M
authors.lastname: Cuttini
authors.forename: Lucilla
authors.initials: L
authors.lastname: Ravà
authors.forename: Silvia
authors.initials: S
authors.lastname: Rinaldi
authors.forename: Carla
authors.initials: C
authors.lastname: Brusco
authors.forename: Paola
authors.initials: P
authors.lastname: Cogo
authors.forename: Nicola
authors.initials: N
authors.lastname: Pirozzi
authors.forename: Sergio
authors.initials: S
authors.lastname: Picardo
authors.forename: Franco
authors.initials: F
authors.lastname: Schiavi
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Raponi
mesh_terms: D000293:Adolescent; D017677:Age Distribution; D006348:Cardiac Surgical Procedures; D002648:Child; D002675:Child, Preschool; D005260:Female; D005500:Follow-Up Studies; D006331:Heart Diseases / Q000401:mortality* / Q000601:surgery; D017052:Hospital Mortality / Q000639:trends; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D015278:Intensive Care Units, Pediatric / Q000706:statistics & numerical data*; D007558:Italy / Q000453:epidemiology; D007902:Length of Stay / Q000639:trends; D008297:Male; D010343:Patient Admission / Q000639:trends; D010351:Patient Discharge / Q000639:trends; D011446:Prospective Studies; D012372:ROC Curve; D012307:Risk Factors; D012720:Severity of Illness Index; D062606:Tertiary Care Centers / Q000706:statistics & numerical data*